Method and arrangement in the heating of electric furnaces



Sept. 4, 1956 P. H. c. LA BURTHE 2,

METHOD AND ARRANGEMENT IN THE HEATING OF ELECTRIC FURNACES Filed March16, l953 ELECTRICAL CONNECTOR Al A2 /B! B2 )Cl CE l l I l VA VOLTAGEBETWEEN AISTAZ FIGTI VA VOLTAGE BETWEEN Al a A2 m3 vB VOLTAGE BETWEENB1882 FIB: VB VOLTAGE BETWEEN Bl a B2 was vc VOLTAGE BETWEEN c1ac2 FIG.|vc VOLTAGE BETWEEN Cl a c2 Flea VD VOLTAGE BETWEEN DBIAI FIGJ VD VOLTAGEBETWEEN A28Bl F|G.3

INVENTOR.

F f; PIERRE HENRI LABURTHE BY 7 WM ATTOR E YS United States PatentMETHOD AND ARRANGEMENT IN THE HEATING OF ELECTRIC FURNACES Pierre H. C.La Burthe, Paris, France, assignor to Societe Anonyme des Manufacturesdes Glaces e t Produrts Chimiques de Saint Gobain, Chauny & Carey,Paris, France Application March 16, 1953, Serial No. 342,587

Claims priority, application France March 15, 1Q52 15 Claims. (Cl. 13-6)The present invention concerns an arrangement for heating electricalfurnaces by Joule effect and more especially glass furnaces.

It particularly relates to a heating method by polyphase currents,particularly triphase.

It is known that in a triphase mounting the three conductors should becharged equally in order that the resultant of the three voltages bealways null without any current circulating in the coils of the supplytransformer.

Thus, the current which circulates in a furnace between each group ofelectrodes, which is fed by two of the three conductors, should have thesame intensity. Consequently the total power evolved in a glass meltingfurnace, for example, is distributed a priori in the furnace betweendifferent zones located between pairs of electrodes, and saiddistribution cannot be modified during the operation of the furnace.Thus, the management of the furnace lacks flexibility and the quantityof glass produced vanes, because any variation of the rate at which theraw materials are loaded into the furnace produces a local variation ofthe temperatures which, in its turn, modifies the local conductivity ofthe glass bath and consequently requires a change in the distribution ofpower.

The arrangement which is the object of my 1nvent1on, copes with thisdrawback and gives other advantages which will be described hereinafter.It consists in using in a furnace fed by polyphase currents and for eachof the alternative components of the polyphase system, a voltage whichmay be variable and in using betweentwo special points of the furnacethe resulting voltage from the composition of those variable voltages.

In other words, the furnace is supplied with a plurality of phases, eachof which is independently variable, and in which the circuit is notcompletely closed by electrical connections but in which a gap is left,in the part of the electrical circuit submerged in the melt, between twoelectrodes of adjacent phases, and through this gap a current may bemade to flow from phase to phase. The leads and electrodes thus arrangedproduce a supplementary heated zone in a part of a furnace that wouldnot be directly traversed by the primary current of any one phase, greatflexibility is imparted to the heating of furnaces, and powers ofdifferent magnitude may be used in different phases without risk ofdamaging the transformer by short cut current built up through theplurality of phases.

In a disposition like that, when two electrodes, belonging to twoadjacent phases, are next to each other in the bath, it is favorable toconnect them, so that the two current intensities will differ in phaseby the same angle and the electric load per square unit of theelectrodes will, thus, be smaller than if the phases were completelyindependent. n is the total number of phases.

With the above provisions of unequal voltages, and

ICE

uniform diphasing between phases the geometrical sum of the voltages isnot zero; examples of such systems are in the graphs of Figs. 2 and 4,for three phase systems.

If the circuit was completely closed by electrical connections, such asbetween electrodes A and B in Fig. 1, a current resulting from theunbalanced voltages would circulate through the transformer, and as itmay reach rather high values, would damage the transformer, but theinvention provides a gap in the electrical circuit be tween twoelectrodes of two adjacent phases as at A2 and B1 of Fig. 3. Theresulting voltage, thus, produces a current which flows through theportion of the bath constituting a resistor in the gap.

In Fig. 1, the edges of the gap are the electrodes A1 and C2 which arelocated far from each other. The current, which would circulate betweenthese electrodes, would disturb the establishment of the main lines offorce between the two pairs of electrodes. A feature of the inventionconsists in connecting the electrodes C2 with an extra electrode Dlocated next to A1; the resulting current, thus, fiows in the part ofthe bath between D and A1 and gives, as above, a fourth heated zone inthe furnace.

The resulting voltages are applied between electrodes in parts of thefurnace not traversed directly by the currents flowing between the partsof the regular system and produce, in the glass bath, heating currentswhich are different.

The voltage resulting from the composition of the different variablevoltages may be used to produce a heating current through the glass bathin any predetermined zone of the furnace.

An embodiment of my invention, for example in the case of a triphasemounting, consists in feeding three zones of a furnace with threemonophase currents having different voltages the difference in phasebetween two of these voltages being an angle of and in feeding a fourthzone with the voltage that results from the composition of the threedifferent voltages.

The whole constitutes a triphase system.

In the accompanying drawings, Figure 1 schematically illustrates theaforesaid embodiment of my invention, Figure 2 shows the triangle of thevoltages in said embodiment, Figures 3 and 4 respectively representanother embodiment and the triangle related thereto.

Fig. 1 schematically represents a glass melting bank. The pairs ofelectrodes are designated by A1, Az-B1, B2-C1, C2. Each pair has itselectrodes connected to the terminals of one of the three secondarycoils of a transformer of which the primary is not shown. The arrows onthe secondary coils indicate that their voltages are variable. Thisvariation may be obtained by any known means.

The triangle of vectors A, B, C shown in Figure 2 is closed at its twoapexes A and B because electrical connections join A of Fig. l with B1and B2 with C1; and on the other hand, the triangle ABC is opened at itsapex C on account of the inequalities in the voltages at the terminalsof the three phases, so that a residual voltage exists between points A1and C2 of Fig. l.

The above triphase mounting which purposely is unbalanced, by havingadjusted the voltage of the phases individually, would give rise to aconsiderable current of circulation in the coils and would be harmful tothem if terminals A1, C2 were connected by a not very resistantconductor.

But the terminal C2 is connected by a cable to a supplementary electrodeD which may be placed near the loading zone. The residual voltagebetween the electrodes A1 and C2 is applied in those conditions betweenelectrode A1 and electrode D and gives rise to a current which heats theglass therebetween.

if electrodes Cz and D were not interconnected, a current would pass, inthe glass bath, between electrodes A1 and C2 and its lines of electricforce would; impede the lines of electric force established between theelectrodes A1, A2, B1, B2, C1, C2. It is known, indeed, that such linesof force cannot intercross but must find their places along side of eachother.

The residual voltage between the electrodes A1 and D differs accordingto circumstances: it is low when the three main voltages are not verydifferent, but it can become important if they substantially differ fromeach other.

In all cases, the current to which the residualvoltage gives risecontributes to heat the; loading zone, in the case illustrated in Fig.1, keeps up the: fluidity of the glass and consequently insures thenecessary mobility of the medium on which the raw materials float, Thepower which is necessary thereto is low and nearly as. great as thelosses through the walls of the loading zone thus compensating for thoselosses.

There is no drawback to using an excess of electrical energy in the partof the furnace thus supplied because this excess contributes to heat theraw materials.

Said arrangement enables one to control at will. the power spent in thedifferent zones of the glass bath according to the requirements ofparticular zones,. and permits the production of: glass at a temperaturethat doesnot vary with its production.

In the arrangement of Fig. 3, the resulting voltage is used for heatinga zone of the glass bath which is not the loading zone, for example, thezone comprised between the two electrodes Az, B1 which is betweentwozones A1, A2 and B1, B2 heated by the unbalancedv voltages; in thatmounting, the electrode D of the'Figure: 1 is removed and electrode A1is connected to electrode Czby a conductor that is outside the glassbath.

Figure 4 illustrates the voltage triangle of the mounting shown inFigure 3. This triangle is closed at its apexes B and C, owing to theelectrical connections which join B2 with C1 and C2 with A1. On theother hand, the triangle ABC is open at its apex A in consequence of theinequality of voltagesat the terminals of the three phases, whichproduces a residual. voltage between the points A2 and B1.

In the two above described embodiments, the electrodes are horizontal,but vertical or inclined electrodes may be used within my invention.

It is understood that these embodiments. are not re.- strictive; forexample, a greater. number of pairs of elec.--

trodes may be used, with polyphase current. that is other than triphasecurrent.

The following are examples. of the invention:

An arrangement for the heating of electric furnaces by Joule effect andmore particularly of melting glass furnaces, by polyphase currents,which consistsin using for each alternative phase of the polyphasesystem, a volt age which is made variable and in using between twoparticular points of the furnace the residual voltage resulting from thecomposition of said. variable voltages.

A triphase mounting for the heating of electric furnaces by Jouleeffect, and more particularly of melting glass furnaces, which consistsinfeedingthree'zones of the furnace with three monophase currents havingvariable voltages, each voltage being differing of.

in phase from the preceding voltage, and: in. feeding. a.

4 are fed with monophase currents differing of an angle of in phase fromeach other, for example, near. the loading zone.

A triphase mounting according to theforegoing where: in the fourth zonelies between two of the three other zones which are fed with monophase.currents differing of an angle of from each other.

A polyphase mounting according to the foregoing wherein each of thepolyphase phases feeds a zone of the furnace with a monophase current,the variable tension differs of an angle of from the preceding and in.feeding a supplementary zone lying outside the said other zones.

A polyphase mounting according to the foregoing wherein each of thepolyphase phases feeds a: zone of the furnace with a, monophase current,the variable ten.- sion differs. of: an angle. of

from the preceding zone and. feeding a supplementary zone lyingbetweentwo of the said. zones.

What I- claim is:

1. An electric furnace having aplurality of pairs of electrodes, currentsupply means. supplying each pair with a phase ofalternating currentdiffering from each adjacent pair by n being the number of pairs,voltage varying means independently connected to each pair,,electricalconnections other than the melt interposed between adjacent electrodesof certain different pairs, the sole connection. between adjacentelectrodes of another pair being the melt.

2. An electric furnacehaving. three pairs of' electrodes, means tosupply each'pair with a phase of'alternatingcurrent differing by fromits adjacent pair, connecting means other thanthe melt connecting theadjacent electrodes of two phases,

the third phase having an electrode adjacent anelec-- trode of anotherphase'hut connected-thereto only'by'the melt, and means to vary thevoltages of the phases individually whereby to flow current through themelt between those electrodes of the different phases which areconnected only by the melt;

3. An electric furnace for the heating of' molten materials by thepassage therethrough of electric current introduced by electrodeswhichcomprises a tank adapted to hold the molten materials, a pluralityof pairs of' electrodes adapted to engage the molten materials, means tosupply one pair of electrodes with alternating current, a second pair ofelectrodes: adjacent the said one-pair in said furnace, means to supplysaid second pair with alternating current. differing in phase by phases,an electrical. connection other than. the molten. materialsconnectingadjacent. electrodes of: the first and.

second pair, one electrode of. said one pair being adjacent an electrodeof another phase andelectrically connected thereto solely by the moltenmaterial, voltage varying means connected to a said pair of electrodescarrying a said phase, and independently variable voltage varying meansconnected to a pair of electrodes carrying another phase.

4. The method of heating molten materials by the passage of electriccurrent therethrough that comprises passing through a plurality of pathsin said molten materials a plurality of phases of alternating currentdiffering from each other by about n being the total number of phases,producing unbalanced voltage in at least one said phase, and flowingsuch unbalanced voltage through said molten material from one phase toanother;

5. A method for heating the contents of a melting furnace by electriccurrent passing through the molten charge which comprises passingseparate phases of current through separate paths in the moltenmaterials, said phases differing from each other by n being the totalnumber of separate phases, controlling the voltage of each phaseseparately and thereby producing an unbalanced voltage, and passing saidunbalanced voltage through a portion of the melt other than said paths.

6. A method according to claim 4 in which there are three phases passingthrough three paths, in Which the currents differ in phase by and inwhich the unbalanced voltage is passed through a fourth path. 1

7. A furnace according to claim 1 in which an extra electrode isimmersed in the melt, in proximity to an electrode of one phase, and isconnected with an electrode of a different phase.

8. The method of heating a molten mass that comprises passing aplurality of phases of electricity through it, unbalancing the phases,and passing the unbalanced current through a part of the molten mass notdirectly traversed by the current of the said phases.

9. An electric furnace having n pairs of electrodes, current supplymeans supplying each pair with a phase of alternating current withvoltage differing from the pre ceding one by varying means independentlyacting on each phase voltage, electrical connections other than the meltinterposed between adjacent electrodes of certain successive pairs, thesole connection between adjacent electrodes of another pair being themelt.

10. An electric furnace having three pairs of electrodes, means tosupply each pair with single phase alternating current differing involtage from each other pair by 120, connecting means other than themelt between the adjacent electrodes of two pairs, the third pair havingan electrode adjacent an electrode of another pair but connected theretoonly by the melt, and means to vary the voltages of the three phasesindividually, whereby to flow the resulting current through the meltbetween those electrodes of the difieernt pairs which are connected onlyby said melt.

11. An electric furnace for the heating of molten materials by thepassage therethrough of electric current introduced by electrodes, whichcomprises a tank adapted to hold the molten materials, It pairs ofelectrodes adapted to be immersed in the molten materials, means tosupply from the preceding voltage phase, an electrical connection otherthan the molten materials connecting electrodes of two pairs, anelectrode of said one pair being adjacent an electrode of another pairand electrically connected thereto solely by the molten material,voltage varying means connected to one of said pair of electrodes andindependently variable voltage varying means connected to the secondpair of electrodes.

12. A method for heating the content of a melting furnace by electriccurrent passing through the molten charge which comprises passingseparate phases of current through separate paths or" the moltenmaterials, the voltages of each phase differing from the preceding onethrough an angle of n being the total number of phases of current,controlling the voltage of each phase separately and thereby producing acurrent of which the voltage is the result of the n. unbalance voltages,and passing said current through a portion of the melt other than saidpaths.

13. A method according to claim 12 in which there are three phases ofcurrent passing through three paths, the voltages of the three phasesdiffering by 120 degrees, and in which the current produced by thevoltage resulting from the unbalancing of the voltages of the threephases is passed through a fourth path.

14. A method for heating the content of a melting furnace, by electriccurrent passing through the molten materials, said current beingsupplied by a plurality of n phases of alternating current, which nvoltages difler in phase through an angle of phase, and using thevoltage resulting from the composition of the unbalanced n voltages ofthe different phases in a portion of the bath not already traversed byany one of the :2 phases.

15. A method for heating three zones of a melting furnace whichcomprises passing three phases of alternating current through the melt,of which the voltages differ in phase through an angle of degrees, andare of unequal value, separately controlling the phases, and heating afourth zone by the current resulting from the composition of the threeunequal voltages.

References Cited in the file of this patent UNITED STATES PATENTS1,244,415 Booth Oct. 23, 1917 1,478,375 Bennett Dec. 25, 1923 1,997,524Kuntzinger et al Apr. 9, 1935 2,089,690 Cornelius Aug. 10, 19372,225,617 Borel et a1. Dec. 24, 1940 2,267,537 Romazzotti Dec. 23, 19412,277,679 Borel Mar. 31, 1942 2,397,852 Gentil Apr. 2, 1946 2,413,037 DeVoe Dec. 24, 1946 2,490,339 De Voe Dec. 6, 1949 2,545,619 Lambert Mar.20, 1951 2,600,490 De Voe June 17, 1952 2,636,913 Lambert Apr. 28, 1953FOREIGN PATENTS 245,610 Switzerland Aug. 1, 1947

